New Zealand
26 January 2010

AgResearch has discovered the clover root weevil (CRW) on the Taieri Plain. AgResearch scientists are currently sampling local farms to see how well established the pest is in the area, before deciding how to address the infestation. AgResearch Scientist Dr Barbara Barratt says the weevils are small and hard to see, but farmers can assist by informing AgResearch if they see the typical weevil feeding damage on their white clover.

The larvae of this pest can devastate pasture by eating the clover root and killing the plant. The adults feed on white clover leaves producing a characteristic ‘notching’ of the leaf margin. Up to 1500 weevil larvae per square metre were counted in the soils underneath Waikato pastures in 1997, and this dramatically reduced clover content.

AgResearch scientists have released a tiny wasp from Ireland as a biological control agent for CRW. The wasp has been used successfully in the North Island to control this pest. The wasp lays its eggs in the weevil, thereby making it sterile. However, it is important more is understood about the distribution of CRW on the Taieri before we consider how we tackle the pest in the area.

Clover root weevil, Sitona lepidus, was first discovered in 1996 in Waikato and Auckland, and by 2004 it had spread throughout the North Island. In April 2006, AgResearch found a large population of CRW established in dairy pasture at Richmond, near Nelson, and it has been detected at Clinton. “The arrival of the weevil on the Taieri Plain is disappointing but inevitable” said Dr Barbara Barratt.

Farmers who identify CRW damage on their properties should contact Colin Ferguson at colin.ferguson@agresearch.co.nz  

http://www.agresearch.co.nz/crw/#intro
 

Website: http://www.agresearch.co.nz

Published: January 26, 2010